A solar cell that converts sun light directly into electrical energy has been attracting attention as a means of supplying clean and inexhaustible energy and has been studied in various fields.
Generally, the performance of a solar cell is evaluated by conversion efficiency that is a percentage of electrical energy converted from incident light energy of the sun. The incident light energy is light energy that has been absorbed into a cell (photovoltaic element) inside a solar cell, and thus the conversion efficiency depends on the ability (absorption ability) of a cell to absorb light energy incident on the cell, and the absorption ability varies significantly depending on the performance of the cell used.
For example, sun light has a broad wavelength range including ultraviolet light, visible light and infrared light, but not all these lights upon incident on a solar cell are converted into electrical energy, and only light in the wavelength range which can be adsorbed by the cell can be converted. Light in the wavelength range adsorbed by a cell is determined by physical properties inherent in the cell, where the peak wavelength in spectral irradiance distribution of sun light is in the vicinity of 500 nm, while when a crystalline silicon cell is used, the peak wavelength of spectral sensitivity thereof is in the range of 600 to 1000 nm, and thus sun light cannot be sufficiently adsorbed and the efficiency of conversion of sun light into electrical energy is inevitably lowered. Accordingly, it is an important task for the solar cell to improve conversion efficiency by absorbing as much sun light as possible.
A solar cell using a crystalline silicon cell is known which includes a module structured such that a front cover is arranged at the side of a light-receiving surface and a back cover at the other side, and a crystalline silicon cell is sealed with a sealing material between the covers (JP 6-177412 A). A fluorescent film-forming ink composition is proposed in which an inorganic fluorescent material and an ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVA) have been dissolved in a solvent (JP 8-102257 A), and a composite panel is proposed in which EVA has been compounded with a luminescent pigment and an inorganic light-accumulating fluorescent material (JP 2004-249644 A), but as a solar cell module-sealing material, there is not known a combination of a fluorescent material and EVA.
In these fluorescent materials, however, when a rare earth metal inorganic material is used as a fluorescent substance, the transparency of EVA is significantly inhibited, while when an organic material is used as a fluorescent substance, thermal deterioration is significant with insufficient durability, and thus the combination of the fluorescent substance and EVA has been disadvantageous and practically problematic.